AU602452B2 - Water proof dust proof structure in electric tool - Google Patents

Description

I111 ii*l*---iEl- Mi-L~ilII* )_LIEII3 ICI S F Ref: 98036 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: 0245 Class Int Class Complete Specification Lodged: Accepted: Published: Priority: Related Art: j Name and Address of Applicant: Address for Service: Ryobi Ltd.

No. 762, Mesaki-cho Fuchu-shi Hiroshima-ken

JAPAN

Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: *9 a Water Proof Dust Proof Structure in Electric Tool The following statement is a full description of this invention, incllding the best method of performing it known to me/us 5845/3 Kr

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ABSTRACT OF THE DISCLOSURE A water proof dust proof construction adapted to be detachably installed on an electric tool for spacedly covering an air intake port of the electric tool. The water proof duct proof construction includes a filter and a filter supporting means. The filter has an effective filtering area which is capable of passing sufficient amount of air to pass therethrough which amount is equal to or larger than air sucking performance of a motor fan. Therefore, air is smoothly introduced into a motor case through the filter and through the air intake port.

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I ,i L WATER PROOF DUST PROOF STRUCTURE IN ELECTRIC TOOL BACKGROUND OF THE INVENTION The present invention relates to a water proof dust proof construction in an electric tool such as a cutter, a grinder and a circular saw.

In an ordinary available electric tool, for cooling a drive motor, an external air is introduced into a motor case through an air intake port by a rotation of a motor fan S coupled to a motor shaft in order to avoid overheating of the motor, and the air is discharged outside through an air discharge port.

One conventional electric tool, for example, a circular saw will be described with reference to Fig. 5. A motor 3 is accommodated in a motor case 1, and a gear case 2 which accommodates therein a power transmission mechanism (not shown) has one side end provided to a front end portion of the motor case. The gear case 2 has another side provided with a protection cover 10 so as to cover an upper portion of a cutter 5 connected to the power transmission mechanism.

Further, a base plate 9 is provided at a lower face of the motor case 1, and a handle 4 is provided at an upper face of the motor case 1. A fan 6 is connected to a motor shaft 3a within the motor case, and an air discharge port 8 is provided at a position between the motor case 1 and the gear case 2, and further, an air intake port 7 is formed at a 1Arear wall of the motor case.

When the motor 3 is drivingly rotated, the cutter 5 is rotated for performing an intended cutting operation.

Simultaneously, the fan 6 is rotated, so that the external air is introduced into the motor case 1 through the air intake port 7 for cooling the motor 3. The air is then discharged through the discharge port 8. Incidentally, a cooling liquid L is injected onto the cutter, if necessary, during the cutting operation.

i a,, d, <Fig. 6 shows another conventional electric tool such as t a circular saw, wherein like parts and components are designated by the same reference numerals as those shown in Fig. 5 for avoiding dupliate description. In this electric tool, a brush cap 14 is threadingly engaged with a hollow brush holder 15 fixed to the motor case and a known carbon brush 16 is disposed slidably with respect to a sleeve portion 15a of the brush holder 15. A compression spring 19 is disposed in the sleeve portion 15a so that the brush 16 is urged toward a commutator 18 of the motor 3. The carbon brush 16 is normally in contact with the rotating commutator 18 for providing an electrical connection between a field coil 20 and an armature 21. In the conventional device, a head 14a of the brush cap 14 is exposed to the 0 atmosphere at the motor case 1' Therefore, even if the carbon brush 16 is frictionally worn, the brush cap 14 can be easily disassembled from the brush holder 15 for 2 i facilitating replacement of a frictionally worn brush 16 by a new brush.

In the above described conventional electric tools, if a workpiece is subjected to cutting while applying cooling or lubrication liquid L onto the cutter, or if the electric tool is used in rainy atmospheric condition, water or cutting chips generated at the cutting operation and other ambient dusts may be entered into the motor case 1 through the air intake port 7. The thus intruduced water, chips and dusts may affect service life to a bearing portion of the motor 3, or short circuit or insufficiency in electrical insulation may occur by these foreign objects to thus cause elecrical shock and thermal seizure of the motor. Further, by the water or dust invasions, motor cooling is not sufficiently achievable.

Further, in the device shown in Fig. 6 in which end faces of the brush cap 14 and the brush holder 15 are exposed from the motor case 1, if minute gap is provided between the outer peripheral surface of the brush holder and motor case 1' or if minute threading clearance is provided between the brush holder 15 and the brush cap 14, water may be entered into the motor case 1' through the minute gap, to thereby lead to the above-described accident such as short circuit.

SUMMARY OF THE INVENTION The present invention has been established in view of -3- L7-73 the above described problems, and it is an object of this invention to provide a water proof dust proof construction for use in an electric tool, the construction being capable of eliminating, with an extremely simple construction, entry of water and/or dust into a motor case, to thereby avoid insufficient cooling to a motor, thermal seizure of the motor, frictional wearing of a bearing portion and electrical short circuit.

In order to attain the above described object, in the present invention, there is provided a water proof dust proof structure in an electric tool, the electric tool including a motor case accommodating therein a motor and having one end formed with an air intake port and another end formed with an air discharge port, and a motor fan disposed in the motor casing and provided coaxially with the motor, air being introduced into the motor case through the air intake port upon rotation of the motor fan and being discharged from the motor case through the air discharge port, the water proof dust proof structure in the electric tool characterized by: a filter having a bag shape for spacedly covering the air intake port, the filter preventing water and dust from passing therethrough but allowing air to pass therethrough; and filter supporting means having a base end mounted over the motor case for supporting the filter and maintaining the bag shape thereof, the filter providing 4 bcY r__ an air venting amount per unit area and per second of X cm 3 /cm 2 /sec and the filter providing an effective filtering 2 area of Y cm and the motor having an air intaking 3 efficiency per second of Z cm /sec, and X Y being larger than or equal to Z.

I In the water proof dust proof construction thus constructed in the electric tool, when the motor is If energized, the fan connected to the motor shaft is rotated, and air (external air) is introduced into the motor case Sthrough the filter and through the air intake port, which 0! 0 a 0, filter is assembled to the motor case in such a manner that a the filter is disposed over the air intake port. The thus 0 introduced air passes through a space defined between the 1, motor and an interior surface of the motor case and is disharged outside through the air discharge port.

a Thus the motor is subjected to cooling by the air continuously introduced into the motor case. In this instance, the rain drops under the cutting operation in rain, scattered cooling liquid at the time of cutting, ambient dusts or cutting chips generated at the cutting operation are prevented from being entered into the motor case by the filter because of the filtering function thereof. The external air for cooling the motor is however j ,4A smoothly and naturally introduced into the motor case since the filter has suffiently large air venting area.

Water and the dusts may adhere onto the surface of the filter. However, the filter itself does not restrain air to pass therethrough for introducing sufficient amount of air for motor cooling, since the air venting effeciency of the filter is still available for the air sucking efficiency of the motor fan. The water or dusts adhered onto the filter are easily removable by wiping these from the filter.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, Fig. 1 is a vertical cross-sectional side view showing a water pzoof dust proof construction in an electric tool according to one embodiment of this invention; Fig. 2 is a cross sectional view taken along the line II- II in Fig. 1; Fig. 3 is a perspective view showing a filter supporting means; Fig. 4 is a vertical cross-sectional side view showing a water proof dust proof construction in an electric tool according to a second embodiment of this invention; Fig. 5 is a vertical cross-sectional side view showing one conventional electric tool; and, Fig. 6 is a vertical cross-sectional side view showing another conventional electric tool.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to this invention will next be described with reference to drawings.

Figs. 1 thru 3 show a water proof dust proof -6- L- construction adapted to be installed on an electric tool according to a first embodiment of this invention. An electric tool per se is the same as the conventional tool shown in Fig. 5. That is, the electric tool includes a motor case 1, a gear case 2, a motor 3, a handle 4, a cutter 5, a motor fan 6, a base plate 9 and a protection cover 10. When the fan 6 fixedly connected to a motor shaft 3a is drivingly rotated by the motor 3, external air is introduced into the motor case 1 through an air intake port 7 formed at a rear wall la of the motor case 1. The thus introduced air passes along a passage A defined between an interior surface of the e motor case 1 and the motor 3 and reaches the motor 3 to cool the same, and the air is dischaged outside through the a discharge port 8 positioned between the motor case 1 and the S" bear case 2.

According to this embodiment, a filter 11 is disposed over a rear barrel portion of the motor case 1 so as to be disposed over the air intake port 7, and the filter 11 is fixedly secured to the barrel portion by a fastening band 12 for avoiding removal of filter.

Further, the filter 11 is formed of a flexible material ii and has a bag shape. Therefore, if only a filter 11 is attached to the rear portion of the motor case 1, the filter is rapidly deformed and is comming into contact with the rear wall la of the motor case 1 or into intimate contact therewith to thereby clog up the air intake port 7, to thus -7degrade air sucking efficiency.

Therefore, in the present invention, a filter supporting means 13 is further disposed over which the filter 11 is inserted for normaly providing a bag shape configuration of the filter, and such bag shaped filter is maintainingly attached to the rear portion of the motor case 1.

Regarding means for maintaining expansion state of the filter 11, there is provided filter support means 13 shown in Figs. 1 thru 3. The filter supporting means 13 as shown o o 0 o has a base sleeve portion 13a attachable over the rear g0 portion of the motor case 1, and a plurality of stems 13b I 0 0o extending in parallel with each other from a rear end face 0 0 0 So 0 of the base sleeve portion 13a and provided spaced apart 0 0 4 .o from each other by a space 13c. Free ends of the stems 13b 0 are connected to an annular portion 13d. Incidentally, ,o0 instead of the plurality of stems, a basket or other relevant members those being capable of air venting and S supporting the filter 11 in its expanding state can be connected to the base sleeve portion 13a.

The filter 11 is mounted over such filter supporting means 13, and the base sleeve portion 13a together with the filter 11 are detachably connected to the rear portion of the motor case 1 by means of the fastening band 12, etc.

Further, instead of the filter supporting member described above, overall filter supporting member can be provided by a wire net or a porous cylindrical sleeve 8 member, and the filter 11 is mounted over the net or sleeve.

Furthermore, the filter and the filter supporting member can be provided integral with each other, and the thus ingtegral member is assembled to the motor case.

Here, the filter 11 must provide the following conditions: The filter must have air venting efficiency which allows air to pass therethrough, but prevents water or dusts from passing thereghrough. If required, the filter has a water repelency; The filter 11 is partly overlapped with the filter 0 o o 0 supporting means. Therefore, the portions other than the 0 0 co overlapping portions can substantially perform filtering oa~ function (hereinafter simply referred to as "an effecitive o 0 filtering area"). Amount of air passable through the S" effective filtering area must at least be larger than air 0 sucking or intaking efficiency provided by the motor fan 6 0 °o provided that no filter is attached to the motor case. If used is a filter havfng insufficient air venting 0 0 characteristic with respect to the air sucking efficiency of o oo0 the fan 6, pressure within the motor case 1 may be lowered, and a negative pressure may be generated. Then, there is more likelihood in that the water or dusts adhere the filter surface, and pressure within the motor case is becoming much more lowered, since effective filtering area is reduced by the adhesion of dusts, water, etc. Finally, the water or 9 0 0 0 00 00 Z o 0 0o the dusts adhering onto the filter surface may forcibly be urged toward the motor case 1 and pass through the filter, to thereby deteriorate filtering function. As a result, no water prc f and dust proof effects is attainable.

In light of the condition the material of the filter 11 is selected from the group consisting of paper, cloth, synthetic fiber, sponge and any combination thereof.

Preferrably, the synthetic fiber is used. If water repelency is provided to such material, it is possible to further prevent water from passing through the filter.

In light of the condition the following relationship is required; X Y Z 3 2 in which, X (cm 3/cm 2/sec) implies an efficiency in air venting amount of the filter per unit area per unit time, Y (cm 2 implies effective filtering area, end Z (cm 3/sec) implies efficiency in air intaking amount of the motor fan 6 pe- unit time.

For example, if the air intaking efficiency Z of the motor fan 6 is 6.3 liters per second, and if the efficiency in air venting amount X of the filter 11 is 9 cm 3/cm 2/sec, 2 the effective filtering area Y must be at least 700 cm If such filter is used, no water or dusts are entered into the motor case 1, and only a required amount of air is smoothly introduced into the motor case 1.

If the filter can be satisfied with the above two 10 conditions, any shape of the filter is available such as cylindrical shape, polygonal shape, and spherical shape.

With the variation of the filter shape, the configuration of the filter supporting means is modified into a shape corresponding to the filter shape.

Further, the base sleeve portion 13a of the filter can be made of a material having a proper resiliency for enhancing sealability at that portion.

With the structure, by the rotation of the motor fan 6, the air is introduced into the motor case 1 through the filter 11 in order to cool the motor 3, and is discharged outside through the discharge port 8. In this case, since the filter prevents the water or dusts from passing therethrough for avoiding entry of these foreign object into the motor case 1, and since the filter provides the effecitive filtering area which allows air to pass therethrough by the amount equal to or larger than the air sucking amount by the fan 6, air is smoothly introduced into the motor case as if no filter 11 is provided.

Next, a second embodiment according to this invention will be described. The arrangement according to the first embodiment is applied to the electric tool which houses therein a brushless motor or to the electric tool in which a brush holder means is not exposed on the motor case in spite of the employment of the motor having the brush such as a I single-phase commutator motor. On the other hand, an 11 arrangement according to the second embodiment is applied to an electric tool in which the brush holding means are exposed on the motor case as shown in Fig. 4. Incidentally, in Fig. 4, like parts and components are designated by the same reference numerals as those shown in Figs. 1 and 6 for avoiding duplicating description.

i According to an electric tool shown in Fig. 4, provided is a brush holding means including a brush holder 15 and a brush cap 14. The brush holder 15 is fixedly secured to the motor case and the brush cap 14 is coaxially and treadingly engaged with the brush holder. And as shown in Fig. 6, in the electric tool, a head portion 14a of the brush cap 14 and a planar end face of the brush holder are exposed at an outer surface of the motor case 1' Therefore, in the second embodiment, attantion is drawn to an axial length of a base sleeve portion 13'a of a filter support means 13', which base sleeve portion is originally adapted to support an open end portion of a filter 11', and the base sleeve portion 13'a has a sufficient axial length ,i .capable of covering the exposed end face of the brush holder 15 and the exposed head portion of the brush cap 14. With this arrangement, water cannot be entered into the motor case through a threading gap which may be defined between the brush cap 14 and the brush holder 15, to thereby obviate personal accident.

Incidentally, in order to cover the exposed portion of 12 r

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L the brush supporting means, the open end portion of the filter 11' or a portion adjacent thereto can be directly positioned over the exposed portion instead of the placement of the filter supporting means thereover. That is, in case where the base sleeve portion 13'a of the filter supporting means 13' does not have an axial length sufficient enough for covering the exposed portion, used is a filter having a part disposable over the barrel portion of the motor case 1' and the part having a length larger than the axial length of the base sleeve portion 13'a. With this arrangement, an inner peripheral surface of the open end portion of the filter can be in direct close contact with the exposed portion.

Apparently, the filter 11' used in the seco3d embodiment is satisfied with the conditions and described in the first embodiment.

Further, the base sleeve portion 13'a of the filter supporting means 13' should preferrably have an inner peripheral shape exactly in conformance with the outer peripehral shape of the rear portion of the motor case 1' and the end face shapes of the brush holder and the brush cap. For this, the base sleeve portion is formed of a material having low elastic modulus such as a plastic material and a rubber, so that the inner peripheral shape of the base sleeve portion can be in confoirmance with the outer 13 S" shape of the rear portion and the end face shapes.

Alternatively, provided that the filter supporting means 13' is formed of a material having high rigidity, a rubber coating is effected onto the inner peripheral surface of the base sleeve portion 13'a, so that the inner surface of the base sleeve portion becomes conformable to the outer profile of the motor case 1' Further, in the second embodiment, the base sleeve portion 13'a of the filter supporting means should preferrably be formed of a material having low friction constant so as to provide easy detachment of the supporting o. means relative to the motor case to thereby facilitate o replacement of the brush 16 by a new brush.

a In the present invention, thus constructed, completely avoidable are the electrical short circuit, insufficient insulation, mechanical breakdown at the bearing portion and thermal seizure of the motor which may be caused by the invasions of water or dusts, since prevented by the filter is the entry of rain drops when operating the tool in rain or entry of scattered cooling liquid during cutting operation, or entry of cutting chips and ambient dusts, aL.d a sufficient amount of air only passes through the filter.

Further, intended filtering function can be easily attainble with simple construction by merely attaching the filter to the motor case in such a manner that the filter is disposed spacedly over the air intake port of the motor 14 s L i ll-^Lurrrll- case.

Furthermore, the water proof dust proof construction in the electric tool according to this invention is easily assembleable to an ordinary available electric tools, and therefore, the arrangement according the invention is economically beneficial.

Moreover, in the water proof dust proof construction according to this invention, external air can smoothly pass through the filter, and therefore, water or dusts adhered onto the filter surface can be easily removed.

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Claims (1)

1. 2. The water proof dust proof construction in the electric tool as defined in claim 1, wherein the electric 16 4 tool further includes a brush holding means having an end face exposed to an atmosture at the barrel portion of the motor case, and the end face is air-tightly covered with at least one of the filter supporting means and the filter. i 3. The water proof dust proof construction in the electric tool as defined in claim 1, wherein the filter has a flexibility, and wherein the filter supporting means comprises a base sleeve portion disposed over the barrel portion, a plurality of stems extending in parallel with g each other from a rear end of the base sleeve portion, the 0o 0 filter being disposed over the plurality of stems and the 0o base sleeve portion, whereby the bag shape of the filter is maintainable. DATED this FIFTH day of JUNE 1989 Ryobi Ltd. Patent Attorneys for the Applicant SPRUSON FERGUSON i 1